Screen printing apparatus



Sept. 3, 1963 M. H. SHERMAN SCREEN PRINTING APPARATUS Filed July 20, 1959 3 Sheets-Sheet l INVENTOR MAM/c5 H Swen/w ATTORNEY! null'lunlll'ailoroul p 3, 1963 M. H. SHERMAN 3,102,469

SCREEN PRINTING APPARATUS Filed July 20, 1959 s Sheets-Sheet 2 INVENTOR Mwe/cs H $HEM4N ATT RNEY M. H. SHERMAN SCREEN PRINTING APPARATUS Sgpt. 3, 1963 3 Sheets-Sheet 3 Filed July 20, 1959 INVENTOR ATTORNEY) 3,102,469 Patented Sept. 3, 1963 United States Patent Office 3,102,469 SCREEN PRINTING APPARATUS Maurice H. Sherman, 278 Keller St., Monterey Park, Calif. Filed July 20, 1959, Ser. No. 828,259 6 Claims. (Cl. 101-122) material passing thereunder.

An object of my invention is to provide a screen printing apparatus, employing silk or other mesh materials in the printing screen, of the type in which the printing screen is arranged in an endless flexible belt, as contrasted to printing screens utilizing flat rigid frames.

Another object of the invention is to provide an end lessabelt printing screen apparatus which subjects the screen to uniform tension, both laterally and longitudinally, throughout its service life.

It is also an object of the invention to provide a method and means for effecting the transformation of a printing screen from its flat configuration, as received in a frame from the artist or workman who has imparted the desired design to the stencil material of the screen, into the endless-belt configuration suitable for mounting on the rollers of a high-speed printing apparatus, while preserving in the endless belt the uniformity of tension imposed on the screen in its flat configuration. The possibility of distortion of the work of the artist is thereby avoided and faithful reproduction thereof assured. In addition, the endless-belt printing screen can be preserved for re-use, inasmuch as tension is maintained on the screen during storage of the belt, as well as so long as the belt is mounted in the printing apparatus.

A further object of the invention is to provide an endless-belt screen printing apparatus for economically producing high-speed short runs of printed web material by the use of endless-belt printing screens of a disposable nature which are quickly and economically made from the flat framed screen prepared by the artist. Apparatus embodying my invention also provides means for readily acornplishing a change in setup from one disposable belt to another and includes belt-driving and tensioning means of a permanent nature to which a belt can be connected and disconnected quickly.

Yet another object of the invention is to provide a screen printing apparatus utilizing an endless-belt printing screen mounted in longitudinal tension on rollers, the opposite sides of the belt including flexible metal bands which carry bearings guided in yokes or tracks and adapted to laterally tension the screen.

A still further object of the invention is to provide an endless-belt screen printing apparatus including flexible metal side bands having a positive drive connection with the rollers on which the endless-belt printing screen is mounted to maintain accurate registry of the stencil with the web being printed, particularly in multi-color apparatus.

These and other objects and advantages-of my invention will be apparent from the following description when taken in conjunction with the annexed drawings in which:

FIGURE 1 is a perspective View of a printing head embodying my invention;

FIGURE 2 is a schematic longitudinal sectional view on the line 22 of FIGURE 1 and additionally showing a feed-belt mechanism for a Web of material to be printed by the printing head;

FIGURE 3 is a vertical sectional view taken through the axis of tone of the screen-supporting rollers of the printing head as viewed on the line 3--'3 of FIGURE 2;

FIGURE 4 is a vertical sectional view on the line 44 of FIGURE 2 showing the manner in which the printing head can he opened up for the replacement of a printing screen;

FIGURE 5 is a fragmentary elevational view, partly in section, of the lateral tensioning means for the printing screen and also showing the details of the connection of the printing screen to the lateral tensioning means;

FIGURE 6 is a fragmentary perspective view showing some of the parts of FIGURE 5 in exploded relationship;

FIGURE 7 is a perspective view illustrating one step in the fabrication of an endless printing screen according to any invention;

FIGURE 8 is a perspective view showing another step in the fabrication of the endless printing screen;

FIGURE 9 is a partial perspective view showing another embodiment of the invention; and

FIGURE 10 is a partial elevational view, with portions in cross section, of yet another embodiment of my invention.

For clarity, the drawings illustrate but one printing head embodying my invention, but it is to be understood that the invention is adapted for and, in fact, has particular advantages in multi-color printing apparatus utilizing a plurality of printing heads; it will he apparent from the following description that the stencils of the several endless printing screens are precisely maintained in accurate synchronization with one another for precise hairline registration with thepattern or design to be imprinted on the web passing through the apparatus. It will also be appreciated that the material onto which the design is transferred is not necessarily a fabric, the screen may be made of other materials than silk, and also that the medium transferred through the screen can be something other than ink.

In general, each printing head comprises a rigid framework 20 mounting a pair of parallel rolls 21 at opposite ends thereof. An endless printing screen belt assembly 22 is sleeved around both rolls 21 to be suported thereby and at least one of the rolls is adjustable towards and away from the other of the rolls to impose a longitudinal tension on the belt assembly 22'.

An endless feed belt 25 is mounted directly beneath the framework 20 on three supporting rolls 26. The two end rolls 26 have their axes disposed in a plane which is offset beneath the axis of the central roll 26. A web 27 of material to be printed is fed into one end of the apparatus onto the feed-belt 25 and in its passage over the central roll 26 is brought into contact with the endless printing screen .belt assembly 22. The framefork 20 mounts a squeegee 28 which is positioned between the rolls 21 in a position to force ink from a supply means 29 through the bottom flight of the belt assembly 22. The rolls 21 and rolls 26 are synchronously driven, preferably by a positive drive connection so that the speeds of the belt assembly 22, feed-belt 25 and web 27 are the same. The squeegee 28 is positioned immediately above or slightly downstream of the zenith of the central roll 26 so that the web 27 is nipped along a line of contact extending laterally across the screen belt assembly 22, the web thereafter being guided outwardly in a plane which immediately separates .from the plane of the lower flight of the belt assembly 22. Conventional doctor blades (not shown) are mounted in operative association with the rolls 21 to maintain them in a clean condition.

More specifically, the belt assembly 22 has the configuration seen in FIGURE 8 when mounted in the printing apparatus and consists of a sheet of silk 31 framed by a pair of side bands 32 and at least one lateral band 33. In addition to the belt assembly 22, FIGURE 8 also shows a pair of endless drive bands 34, 1 each of which is connected along one continuous edge to an edge of one of the side bands 32.

In making a stencil it is customary for the artist or designer to stretch the sheet of silk 31 in a rigid rectangular frame 36 such as is shown in FIGURE 7, care being taken not to distort the warp and woof of the mesh material. The stencil material is then affixed to the mesh by any of the conventional means known to the art, care being taken, however, to keep the design within predetermined limits of the area of the sheet of silk 31. After the design or stencil has been completed the screen 31 and frame 36 are delivered as an integral unit to the user.

The design area of the silk 31 is conventionally of predetermined dimensions according to the nature of the material to be printed and this is particularly true of the repeat dimension. According to my invention this predetermined area is provided with an auxiliary framework of very thin metal bands applied to the screen 31 while the screen is yet in its prestressed condition within the frame 36. These bands are fastened to the screen 31 and to each other to provide a semi-rigid auxiliary framework adapted to prevent relaxation of the stressed silk screen 31 after being cut out of the frame 36.

' In making the belt assembly 22 a perfectly rectangular framework is first made up of a pair of the side bands 32 and a pair of lateral or end bands 33. All of these bands are made of a very thin sheet metal material, preferably a spring steel, and are fastened together at the cornerswith rivets or other suitable fastening means. One side of the rectangular framework thus formed is then coated with a suitable adhesive and the framework then placed on the tautly stretched screen 31 within the frame 36 in a manner to contain the stencil.

Afterthe adhesive has set, the material of the screen 31 is out along the outer edges of the bands 32 and 33. In removing the rectangular metal frame and the screen 31 framed therein from the original piece of screen it is preferable to commence cutting first along one end band 33 and then along both side bands 32, at the same time rolling the assembly into tubular configuration. Thus, as the assembly 22 is detached from the frame 36 along the remaining or other end band 33 the assembly 22 is already in tubular configuration whereby any buckling tendency of the bands 32 and 33 is avoided and the screen 31 is maintained in the prestressed condition which it had in the frame 36, and the stencil material will also reinforce the silk or other mesh against buckling. As used herein, a pre-stressed screen shall be understood to mean a screen assembly in which the side bands and at least one lateral band shall have been aflixed to the screen when the screen is stretched, as in the frame 36, while the warp and woof elements are tensilely stressed.

'Ilhetwo end bands 33 can then be superposed and fastened together by rivets. Alternatively, the two end bands 33 can be placed alongside one another with their innermost edges in abutment and an adhesive applied to the innermost end hand through the covering layer of screen material. After the adhesive has set, the other or outermost end band is cut away from the assembly along its innermost edge whereby opposite ends of the screen 31 are both adhesively aflixed to the remaining end band 33. This latter procedure has the advantage of providing a seam of minimum thickness. According to either method of forming the belt assembly 22 the assembly isrolled into tubular or endless-belt configuration with the screen 31 on the outwardly facing sides or surfaces of the side bands 32.

One of the rolls 21 mounted in the framework 20 is adjustable towards and away from the other roll 21 so that after the assembly 22 is sleeved thereover a proper longitudinal tension can be maintained on the assembly. In addition, the framework 20 supports a laterally adjustable harness or yoke designated generally by the numeral 40, and a laterally immovable yoke designated generally at 41. These yokes extend longitudinally of the framework 20 on opposite sides of the belt assembly 22 and each of the drive bands 34 is provided with a plurality of roller assemblies 42 engageable with the yokes and adapted to laterally tension the belt assembly 22.

The framework 20 on one side comprises a pair of horizontally extending upper and lower channels 44 and 45, respectively, interconnected at their opposite ends by a pair of vertically extending plates 46. The other side of the framework 20 comprises a horizontally extending relatively Wide side plate 47 and the opposite sides of the framework 20 are interconnected by suitable crossbraces 48. a The vertical spacing between the pair of channels 44 and 45 is sufficiently great to conveniently permit sleeving the belt assembly 22 over the rolls 21, and the spacing between the end plates 46 is sufiiciently long to permit spacing-apart of the rolls 21 for accommodating belt assembles 22 of various lengths.

Each of the rolls 21 is mounted on a shaft 50 which is provided with a removable bearing support at its end in the open side of the framework 20 whereby the bearing support can be swung out of the way to permit sleeving of the assembly 22 over the rolls. Thus, the far roll 21 (as viewed in FIGURE 1) has the removable end of its shaft 50 supported in a pillow block 51 that is mounted on top of a bracket 52. This bracket is in turn hingedly connected as at 53 to a support block 5a, which in turn is mounted for longitudinal adjustment on the bottom channel 45 of the open side of the framework 20.

The pillow block 51 includes a self-aligning bearing '56 swivelly mounted therein whereby the adjacent end of the shaft 50 can be slipped into or out of the bearing 56 upon pivotal movement of the bracket 52. To maintain the bearing in erect, operative position, a suitable fastener 57 is provided for rigidly securing the bracket 52 to the support block 54, and this fastener can be released or engaged through a suitable aperture 58 formed in the wall of the bracket 52. A pair of set screws are provided in the support block 54 for releasable engagement with the bottom channel 45 in order to maintain the bearing assembly in the desired position.

The bearings for the other ends of the shafts 50 are supported in the side plate or channel 47 and FIGURE 3 best illustrates the manner of mounting the shaft '50 of the far roll 21. The side plate 47 is formed with a longitudinally extending central slot 60 whose opposite horizontally extending edges slidably support complementary shoulders of a clamping block 62, disposed on the inside of the side plate 47. The clamping block 62 is provided with a central bore adapted to receive a bearing housing 63 that is provided with a flange 64 adapted to engage the outer surface of the side plate 47. A plurality of bolts 65 are passed through the flange 64 for threaded engagement with the clamping block 62 so that the bearing assembly can be clamped into the desired position within the slot 60. The housing 63 encloses a suitable bearing 66 of relatively great axial length so that sufficiently firm support will be provided for the shaft 50 and the roll 21 thereon when the removable bearing assembly at the other end of the shaft is detached from the shaft.

The shaft 50 of the near roll 21 can be supported by a similar bearing arrangement; however, in order to provide a means for finely adjusting the longitudinal tension imposed on the belt assembly 22 I have provided another type of bearing support for the front roll 21. Conversely, both rolls 21 can be supported by the bearing means presently to be described.

The detachable bearing support for the near roll 21 includes another support block 54 adjustably slidably mounted on the lower channel 45 and securable in place by set screws 55. A bracket 70 is hingedly mounted as at 53' on top of the support block 54 and has a rectangular opening 71 extending laterally therethrough formed work 20. The bearing block 72 on its inner face mounts a self-aligning bearing unit 75, which is of the flanged tylpe, suitable fasteners passing through the flanges for connection of the bearing unit to the bearing block 72.

The bearing assembly can thus be engaged and disengaged from the adjacent end of the shaft 50 and the near roll 21 finally adjusted with respect to the far roll 21 by suitable rotation of the crank 74. In order to maintain the bearing block 72 in initially adjusted position, the bracket 70 is provided with a pair of set screws 76 adapted to bear against the block 72 in the ways of the bracket 70.

As is shown in FIGURE 4, the other end of the near shaft '50 is rotatably supported in the side plate 47 in. somewhat the same manner as the corresponding end of the other shaft 50. However, a like screw adjustment means is provided for the bearing housing 63 to shift the housing relative to a clamping block 63a, which is adapted for this purpose.

Each printing screen belt assembly 22- is of a disposable nature. The drive belts 34, however, are permanent portions of the printing apparatus and each apparatus is provided with a number of sets of drive belts, the sets having lengths corresponding to the conventional lengths of repeats.

I-n mounting an assembly 22 in the printing apparatus a pair of drive belts 34 of appropriate length are selected and one first mounted in'the adjustable yoke 40. The other drive belt 34 is attached to one side of the assembly 22 and the assembled parts then sleeved over the rolls 21 for connection of the other side of the assembly to the first-mentioned drive belt 34.

In order to permit connection and disconnection of the drive belts 34- and assembly 22 in this fashion the drive belts are constructed with the fastening means best seen in FIGURES and 6. Each drive band is made of a thin strip of sheet metal, preferably spring steel, and mounts a plurality of inwardly extending tabs 77. Each of these tabs is provided with a pair of downwardly protruding studs 78 adapted for registration with one of a plurality of pairs of apertures 79 formed in the side bands 32 of the assembly 22. As is shown in FIG- URE 5, each of the studs 78 at its tip is formed with a lip 80 and the side-band apertures 79 are slightly elongated in a direction transversely of the side band 32. To interconnect the side band 32 to the drive hand 34 the several pairs of studs 78 are aligned with the several pairs of. apertures 79 and pass therethrou-gh, after which the stud lips 80 can be moved into engagement with the inside of the side band 32'. As is apparent, so long as the pair of drive bands 34- pull oppositely on the pair of side bands 32 the studs 78 will remain securely locked into the apertures 79.

In the apparatus of FIGURE 1 the near roll 21 is driven from a source of power through the medium of a gear head 82 formed on the end of the shaft 50 outwardly of the side plate 47, while the far roll 21 acts as an idler. The gear head 81 is run synchronously through a positive drive mechanism or the like with other printing heads for multi-color operation, and the feed-belt rolls 26 are also synchronously driven with the gear head 81. Both the feed belt 25' and the drive belts 34 are provided with a gear means for translating rotation of the rolls into movement of the feed belt 25 and belt assembly 22,

t and at least one end band 33 which serve to maintain the respectively, which means will be described only with reference to the drive-band mechanism.

Each of the rolls 21 has gear teeth 83 formed at the opposite ends thereof which have an addendum diameter which is the same as the diameter of the roll. Each of the drive bands 34 on its inward face is provided with a plurality of complementary gear teeth or cleats 84 that are adapted to mesh with the gear teeth '83. These cleats may take the form of separate members of metal fused to the drive band 34 or they may *be formed from an elastomeric or plastic material adhesively fastened to the band.

Both of the yoke assemblies 40 and 41 include a pair of horizontally extending, opposed, generally channelshaped members 86 and a pair of arcuately configured, opposed, channel-shaped members 87. The straight channels 86 of the yoke 40 are rigidly interconnected at their opposite ends by a pair of straps 83, as portions of a rigid rectangular framework which is adjustable laterally of the framework 20. The straight channels 86 of the other yoke 41, which is laterally immovable, are interconnected as opposite sides of a parallelogram linkage by a pair of link bars 89, each bar being pivotally connected at its opposite ends to opposite ones of the channels 86.

The two yokes 40 and 41 are interconnected at their opposite ends by a pair of parallel shafts 91, each of which is fastened at one end in one of the end plates 46 and with its other end fastened in the side plate 47. Adjacent one end, each shaft is mounted through the center of one of the link bars 89. Adjacent its other end, each shaft along the portion thereof extending through a strap 88 carries a threaded collar 92, which in turn mounts a take-up nut 93, inwardly of the strap 88. A lock nut (not shown) is mounted on the collar 92 on the opposite side of the strap 88, in order to maintain the strap 88 and, accordingly, the corresponding end of the yoke 40 in an adjusted position spaced apart from the laterally immovable yoke 41. A lock nut 94 threadedly engages each shaft 91 just inwardly of each link bar 89 to releasably hold the yoke 41 in closed condition.

Referring now to FIGURE 5, it will be noted that each straight channel 86 has an inner wall 95 and an outer wall 96 that is of lesser depth than the inner wall. Each of the roller assemblies 42 of the drive bands 34 is adapted to move within the channels 86 and to impose a lateral tensioning force on the band assembly 22 in accordance with the spacing between the yokes 40 and 41. The arcuate channels 87 have a cross-sectional configuration like that of the straight channels 86 andare mounted at opposite ends of the yokes 40 and 41 for adjustment longitudinally of the framework 20 into positions corresponding to the size of the particular band 22 being utilized in the apparatus.

Each roller assembly 42 includes a bolt 100 extending outwardly from a drive band 34. On the opposite side of. the drive band from the bolt head the bolt coaxially mounts a collar 10 1 surmounted by a roller 102, which in turn is successively surmounted by a tubular spacer 1031and a smaller roller 104, the entire assembly being held together by a nut 105. It will be observed that the large roller 102 is adapted to bear only against the inner wall 95 while the small roller 104 is adapted to bear only on the outer wall 96. These rollers may incude ball-bearing means in order to reduce drag and friction.

I have found that this arrangement is extremely well adapted to ensure a uniform lateral tension on the belt assembly 22 throughout its length. This is ensured first of all because of the use of the thin metal side bands 32 originally pre-stressed condition of the screen 31. When the belt assembly 22 is in movement over the rolls 21, the yokes 40 and 41 and roller assemblies 42 prevent any capsizing, buckling or twisting tendencies of the side bands 32, and additionally ensure the maintenance of proper additional lateral tension on the screen 31. It will particularly be noted that the rollers 1'02 and 104 of each roller assembly are adapted to provide a couple or, in effect, a lever arm fulcrumed about the contact of the large roller 102 with the inner wall 95. This arrangement ensures that the bolt 100 will at all times throughout its travel be disposed normally to that portion of the drive band 34 supporting the bolt. The drive band 34, being clamped between the collar 101 and the head of the bolt, is accordingly held against any distortion.

The arrangement just described is also of importance in preventing any localized tension stresses from being imposed on the material of the screen 31. The screen 31 along every edge has each strand thereof fastened to the side bands 32 or an end band 33. While localized lateral tensioning stresses are imposed on the drive bands 34 and on the side bands 32 at the aperture 79, these tensioning stresses are uniformly distributed through the body of the side bands 32 so that each strand of the screen 31 is subjected to the same stress. As a result, no distortion of the stencil pattern on the screen 31 can occur even after long periods of use of the assembly 22, so that a long service life and even repeated uses of the assembly 22 are possible.

For adjustment of the arcuate channels 87 a pair of tabs 107 are afiixed to each of the opposite ends thereof in positions adapted to slidably support the channel along the opposite walls of the pair of straight channels 86 of each yoke. Each arcuate channel 87 is secured in adjusted position by .a fastening means on a flap 108. On the open side of the framework 26} a pair of flaps 108 are each hingedly secured to one of the end plates 46. Although not shown, it will be understood that similar flaps 108 are similarly attached to the side plate 47. Each arcuate channel 87 is provided with an outwardly extending stud bolt 169 adapted to protrude through a slot 110 extending longitudinally of each flap Hi8. After being moved to adjusted position each channel 87 is held in place by a nut 111 on the stud 1G9 which is run up against the flap .108.

FIGURE 9 illustrates an alternative form of construction for the printing screen belt assembly and the supporting rolls therefor. In this arrangement a belt assembly 22a is provided that consists of a screen 31, at least one end band 33, and a pair of side bands 32a. These parts are assembled in the same manner as the corresponding parts of the previously described belt assembly 22. The belt assembly 22a is supported on rolls 21a which, in lieu of the gear teeth 83, in this instance are provided at each end with radially outwardly protruding sprocket teeth 115, adapted for engagement with a plurality of sprocket holes 116 formed in each of the side bands 32a.

The alternative arrangement just described is utilized in a printing apparatus substantially similar to that described previously. In this embodiment of the invention the longitudinal tensioning of the assembly 22a is accomplished, as before, by the spacing of the pair of rolls 21a. The side bands 32a are supported throughout their widths on the rolls 21a. Thus, when the belt assembly 22a is suitably tensioned in the longitudinal dimension the side bands 32a are supported against flexure and are adapted to maintain the laterally pre-stressed condition of the screen 31.

Another alternative embodiment of the invention is shown in FIGURE 10. This arrangement has a belt assembly 22b consisting of a screen 31, at least one end band 33 (not shown), and a pair of side bands 32b, the assembly 22b being made in the manner previously described. The assembly 22b is supported on a pair of perfectly smooth il'OllS 21b.

The printing apparatus includes a yoke along both sides of the assembly 22b comprising an outer plate 120 and an inner plate 121 disposed (by means not shown) in the same plane with the outer plate 120. The outer plate is formed with a longitudinally extending central opening whose edge is congruent to the path or locus of the pitch line of the travel of the side bands 32b and the inner plate 121 is adapted to fit Within this opening, the two plates thus defining a continuous slot 122 complementary to the path of the endless-belt assembly 22b and adapted to receive a side band 32b therethrough.

A plurality of roller assemblies 42b are mounted on each side band 32b jus-t outwardly of the plates 120 and 121. Each roller assembly comprises a bolt 124 extending through a bore formed in the side band 32b and coaxially mounting on opposite sides of the side band a pair of spacers 125 and a pair of rollers 126. A nut 127 is threadedly engaged with one end of the bolt 124 to hold the assembly together. The pair of rollers 126 are adapted to bear against the outer surfaces of the plates 120 and 121 and at least one set of plates is adapted to be laterally adjusted for imparting the desired lateral tension on the screen 31. v

For driving the assembly 2215 a continuous roller chain in driven engagement with a driving sprocket (not shown) is mounted for travel along the pitch line of the assembly 22b and at least one link thereof is provided with a pin 129 that is drivingly engaged to a connector 130 which in turn is drivingly fastened to one edge of one of the bands 32b.

It will be appreciated that the alternative arrangements just described can be utilized in the apparatus of FIG- URE 2 in lieu of the presently preferred embodiment. In any event, the web 27 is temporarily secured to the feed belt 25 in a conventional manner, as by a suitable adhesive or tape, to be driven through the apparatus. The feed belt may carry the web 27 under several synchronized printing heads and it is preferred that at each printing head the feed rolls be adapted to define a pair of flights whose planes are angularly related. Thus, as indicated in FIGURE 2, an approach flight 25a carries the Web 27 into linear contact with the screen assembly 22 over a longitudinal trace of the central feed roll 26. The squeegee 28 rides on the screen 31 over this longitudinal trace to force ink or the like through the screen onto the web 27 during such linear contact. The printed web is then carried on a receding flight 252' out of contact with the screen, immediately after printing to avoid any possibility of smudging, and clear definition of the printed pattern is maintained.

While I have shown and described several embodiments of my invention, 1 wish it to be understood that I do not means to be confined to the precise details of construction herein set forth by way of illustration. It is apparent that many changes and variations may be made, by those skilled in the art, without departing from the spirit of the invention or exceeding the scope of the appended claims.

1. In a screen printing apparatus the combination comprising: a plurality of rolls; a screen maintained in endless configuration by at least one lateral band interconnecting opposite ends of said screen and having a pair of continuous side bands continuously fastened along the continuous opposite edges of said endless screen, said screen and side bands being trained around said rolls; a framework for said apparatus mounting a pair of yokes along opposite sides of said screen; a pair of continuous drive bands trained around opposite ends of said rolls and drivably engaged by said rolls, each of which is detachable and drivingly connected to one of said side bands as a coplanar extension of said side band; and a plurality of rollers carried by each of said drive bands adapted to be guided by said yokes for laterally stressing said side bands in the plane of said side bands, said rollers and pair of yokes being adapted to constrain said drive bands into substantially coplanar relationship with said screen and said yokes having a constant lateral spacing adapted to laterally tension said drive bands, side bands and screen.

2. An apparatus asset forth in claim 1 in which each of said yokes includes a pair of confronting walls and each of said drive bands carries a plurality of pairs of said rollers on a common shaft that is disposed normally to the plane of that portion of the drive band to which said shaft is attached, each roller of said pair bearing against one only of said confronting walls and said pair of rollers being adapted to provide a couple resisting lateral tension stresses in said screen.

, at their ends in said open side of said framework having detachable bearings normally obstructing said open side that are adapted for movement out of said open side upon being detached from said rolls.

5. An apparatus as set forth in claim 1 in which said framework is open on one side to permit sleeving said screen over said rolls through said open side, said rolls at their ends in said open side of said framework having detachable bearings normally obstructing said open side that are adapted for movement out of said open side upon being detached from said rolls, the one of said yokes adjacent the open side of said framework being expandable to release said rollers for removal of the corresponding drive band along with said screen.

6. In a screen printing apparatus the combination comprising: a plurality of rolls; a screen maintained in endless configuration by at least one lateral band interconnecting opposite ends of said screen and having a pair of continuous side bands continuously fastened along the continuous opposite edges of said endless screen, said screen and side bands being trained around said rolls; means to vary the spacing between said rolls to longitudinally tension said screen; a framework for said apparatus including a pair of y'ok-es on opposite sides of said screen each of which continuously parallels the flight of said screen around said rolls; a pair of continuous drive bands drivably trained around opposite ends of said rolls; a plurality of fastener means interconnecting each of said drive bands to one of said side bands, said fasteners being adapted for disconnection of said side bands and drive bands upon opposite inward movement of said drive bands and adapted to laterally tension said side bands and screen upon opposite outward movement of said drive bands; a plurality of rollers carried on each of said drive bands that are guidedly engaged by said yokes, said nollers and yokes being cooperatively adapted to maintain a constant lateral spacing of said drive bands and side bands; means on said framework operatively associated with both said yokes to decrease and increase the lateral spacing b tween said yokes to selectively disconnect said fastener means or to. laterally :tension said screen, respectively; and a plurality of bearings for ends of said rolls in an open side of said framework, said open side being adapted to permit sleeving said screen around said rolls when said bearings are moved out of said open side, said bearings detachably supporting said ends of said rolls and being movably mounted on said framework for movement out of said open side, .the one of said yokes adjacent said open side being expandable to release the rollers of the corresponding drive band to permit passage of said drive band through said open side.

References Cited in the file of this patent UNITED STATES PATENTS 707,579 Gestetner Aug. 26, 1902 1,146,853 Dick lluly 20, 1915 1,546,834 Hanington lluly 21, 1925 2,019,375 Wheelwright Oct. 29, 1935 2,217,366 Hicks Oct. 8, 1940 2,287,122 Norris June 23, 1942 2,302,152 Snyder Nov. 17, 1942 2,608,750 Cluzel Sept. 2, 1952 2,906,201 Blair Sept. 29, 1959 2,949,847 Clonis et a1. Aug, 23, 1960 FOREIGN PATENTS 723,743 Great Britain Feb. 9, 1955 878,054 Germany Mar. 22, 1954 

1. IN A SCREEN PRINTING APPARATUS THE COMBINATION COMPRISING: A PLURALITY OF ROLLS; A SCREEN MAINTAINED IN ENDLESS CONFIGURATION BY AT LEAST ONE LATERAL BAND INTERCONNECTING OPPOSITE ENDS OF SAID SCREEN AND HAVING A PAIR OF CONTINUOUS SIDE BANDS CONTINUOUSLY FASTENED ALONG THE CONTINUOUS OPPOSITE EDGES OF SAID ENDLESS SCREEN, SAID SCREEN AND SIDE BAND BEING TRAINED AROUND SAID ROLLS; A FRAMEWORK FOR SAID APPARATUS MOUNTING A PAIR OF YOKES ALONG OPPOSITE SIDES OF SAID SCREEN; A PAIR OF CONTINUOUS DRIVE BANDS TRAINED AROUND OPPOSITE ENDS OF SAID ROLLS AND DRIVABLY ENGAGED BY SAID ROLLS, EACH OF WHICH IS DETACHABLE AND DRIVINGLY CONNECTED TO ONE OF SAID SIDE BANDS AS A COPLANAR EXTENSION OF SAID SIDE BAND; AND A PLURALITY OF ROLLERS CARRIED BY EACH OF SAID DRIVE BANDS ADAPTED TO BE GUIDED BY SAID YOKES FOR LATERALLY STRESSING SAID SIDE BANDS IN THE PLANE OF SAID SIDE BANDS, SAID ROLLERS AND PAIR OF YOKES BEING ADAPTED TO CONSTRAIN SAID DRIVE BANDS INTO SUBSTANTIALLY COPLANAR RELATIONSHIP WITH SAID SCREEN AND SAID YOKES HAVING A CONSTANT LATERAL SPACING ADAPTED TO LATERALLY TENSION SAID DRIVE BANDS, SIDE BANDS AND SCREEN. 